Abstract

Low root temperature has previously been reported to induce boron (B) deficiency in some species but the mechanism is not entirely clear. Using B‐specific resin to buffer B concentrations in solution, we found that decreasing root zone temperature (RZT) from 27 to 12°C for 6 days depressed sunflower (Helianthus annuus L.) dry matter, root length, root to shoot ratio and B uptake. Boron uptake into the shoots was depressed at 12°C RZT to a greater relative extent than dry matter. Furthermore, B partitioning to young leaves decreased with low RZT, particularly at 12°C RZT. The external B requirement for shoot growth increased with low RZT. Leaf functioning was impaired by low B supply as measured by K+ leakage from the youngest mature leaf blade, whereas it was much less affected by RZT, and there was no effect of RZT on B ‐ adequate plants. By contrast, root function was impaired more by low RZT than low B. Therefore, we predict that higher rates of B application will be required for plant growth when soil temperature is below a critical threshold, which for sunflower was about 17°C. Conversely, practices which increase soil temperature above the threshold may also improve plant B nutrition.